Electronics Protection - Summer 2014 - (Page 10)

Feature Considerations for Powering Military Applications Michael A. Stout, Vice President of Engineering Falcon Electric, Inc. In today's military applications, the diversity of environmental factors that can render a computer-grade on-line uninterruptible power supply (UPS) inoperable is only exceeded by the number and magnitude of power quality related problems that are often encountered. Most on-line UPS products have been designed for installation in a fixed and protected environment with a controlled temperature range of 32°F to 104°F (0°C to 40°C). They can provide reliable operation when installed in a laboratory, office or computer room environment and their price is low. However, many military applications require that the UPS be installed in battlefield environments far more demanding than a computer room. They are subjected to higher levels of shock and vibration, airborne contamination and wider operational temperature extremes. In addition, the UPS needs to provide clean computer-grade output power while operating from extremely polluted power sources. Military-grade commercialoff-the-shelf (Mil-COTS) on-line UPS products provide a viable solution in meeting the demanding requirement of heavy industrial applications. The following is a brief discussion of problems associated with these applications as they relate to the design and construction of a high-performance Mil-COTS on-line UPS. Unstable Power Advanced technology combined with speed and cost of implementation is driving the deployment of equipment used by the today's military. After 911 the military had to diversify and adjust to the realities of global threats. The military's power sensitive, high-tech equipment may be deployed throughout the world on land, sea and air at a moment's notice to react to evolving conflicts. In more and more cases, COTS hardware solutions are readily available for rapid deployment. In the case of a computer system, it may only require installation of the military's proprietary software. In other cases, the equipment may be of a sophisticated microprocessor-based design that demands a clean, reliable power source. Much of the equipment has been designed to operate from a very reliable, domestic 120 Vac, 60 Hertz (Hz) utility power. The power generated in Afghanistan, Iraq, Europe and many other countries is 220 to 240 Vac, 50 Hz. Aircraft and many military land-based mobile generator power systems supply 115Vac, 400 Hz power. The situation gets even more complicated by local generating sources inside the war zone or in poor third-world countries. Aircraft and land based mobile generator systems are subject to disruptive power frequency instabilities and harmonic distortion problems. The power solution needs to be both flexible and multi-functional. In applications where the local utility source is reliable, the power needs to be converted from 220 Vac to 120 Vac along with conversion of the AC frequency from 50 Hz to 60Hz if domestic equipment is to be connected. For most NATO equipment, 120 Vac 10 Summer 2014 * www.ElectronicsProtectionMagazine.com power has to be converted to 220 Vac and the frequency to 50 Hz. In locations where the utility or generator source suffers from poor frequency regulation, the power solution has to provide a reasonable amount of immunity from frequency variations, harmonics, high voltage transients and a wide input voltage range, while maintaining tight output voltage regulation. For aircraft applications, frequency conversion may also be required if unstable 115 Vac, 400 HZ power is the only source available. In locations subject to complete power outages, the incorporation of battery backup assures the equipment's continued operation. Batteries may also be needed to provide power for equipment used in remote locations where no other power is available. To top the list, the solution must be rugged and reliable enough to survive in a wide range of environments. For aircraft applications, the military's move to implementing low cost single-phase COTS equipment into aircraft and other 400 Hz three-phase mobile applications is exacerbating voltage and current imbalance. The primary concern of voltage imbalance is harmonics and the resulting heating effect as well as the reduction in service life of three-phase motors on the same power bus. A small voltage imbalance of 1 percent results in a 5 to 6 percent current imbalance and may be problematic. An active three-phase/frequency converter (figure 1), can be a good solution. The device connects to three-phase, 400 Hz aircraft power. Through the use of double-conversion and Pulse Width Modulated Inverter (PWM) technologies, the converter changes the incoming power to a DC voltage, regulates the DC Figure 1. Falcon Electric's ED-M rackmount freand recreates new quency and phase converter with optional UPS. single-phase, 50, 60 or 400 Hz output power with a ±3% voltage regulation. The frequency converter can typically operate over a wide input voltage range while maintaining a balanced load on the three-phase 400 Hz bus. The converter provides clean, regulated single-phase sinewave power to the critical load. An optional external battery module is available providing several minutes of ride-through in the event of a momentary or sustained loss of aircraft bus power. Due to the amount of power source switching that normally takes place in aircraft applications, the ability of the installed electronic systems and equipment to maintain enough stored energy to ride-through brief interruptions and reliably operate in the environment is essential. The requirements for equipment ride-through are outlined in FAA standard FAA-G-2100G and military standard MIL-STD-704F. All electronic equipment and flight systems installed on aircraft must meet these standards. However, http://www.ElectronicsProtectionMagazine.com

Table of Contents for the Digital Edition of Electronics Protection - Summer 2014

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Considerations for Powering Military Applications
How Thermal Ground Plane and Compact Air-Cooled Heat Sinks are Revolutionizing Thermal Management
Access Control Solutions for Railway Infrastructure
20 Data Center Downtime Study Puts Focus on Maximum Protection
Cooling and Shielding in the Right-Sized Enclosure
Industry News
Calendar of Events

Electronics Protection - Summer 2014